RoboComp Component & Ros Node chatter¶

We will create a RoboComp Component that can communicate with a Ros Node using Ros Middleware.

The Ros Node which we will use can be found here.

Steps for Creating a Component:

Analyze the Ros Node.
Generate an IDSL.
Generate our RoboComp Component.
Run it.

1. Analyze the Ros Node¶

We need to know what messages or services the Ros Node is using. To find out, we are taking a look at the package documentation and the msg and srv directory.

For more info about what are msg and srv directories, visit this tutorial from ROS.

Here is an image.msg example, taken from our Ros Node:

string name
uint32 size
int32[] image

In Talker.cpp:

// %Tag(PUBLISHER)%
ros::Publisher chatter_pub = n.advertise<beginner_tutorials::image>("chatter", 1000);
// %EndTag(PUBLISHER)%

Talker (the Ros Node) publishes this msg through the topic called chatter.

For more info about topics visit this tutorial from ROS.

Now we know we need an IDSL with a structure containing the types of image.msg, and an interface with a topic called chatter.

2. Generate an IDSL¶

Let’s generate our IDSL:

module RoboCompListener{
    sequence<int> imageVector;
    struct Image {
        string name;
        uint size;
        imageVector image;
};

interface chat{
    void chatter(Image img);
    };
};

:heavy_exclamation_mark: The names of the variables must be identical to those used in the message!

We have created a structure image and a topic called chatter.

For more info about IDSL visit this tutorial created by Robocomp.

3. Generate the RoboComp Component¶

Create your .cdsl like this:

import "/robocomp/interfaces/IDSLs/Listener.idsl";
Component listener
{
    Communications
    {
        subscribesTo chat(ros);
    };
    language Cpp;
    gui Qt(QWidget);
};

And use RoboCompDSL to generate your component.

For more info about creating components, look at this tutorial created by Robocomp.

4. Run it¶

To see if everything worked, try to insert this code in your subscribe method:

printf("Name: %s, size: %d\n", img.name.c_str(), img.size);
for(int i=0;i<img.image.size();i++)
    printf("value of img.image[%d] = %d\n", i, img.image[i]);

Launch your component and enjoy!

Error warning:¶

We assume that Talker and roscore are running.

If you get an error like this:

[ERROR] [1471018647.418758838]: Client [/listener] wants topic /chatter to have datatype/md5sum [RoboCompListener/Image/**5d96ac93c863cbaa85815010f7256b9a**], but our version has [beginner_tutorials/image/**163b37c985fb24d5121dd98a6a240a84**]. Dropping connection.

Then you have not generated an identical message structure.

RoboLab Docs documentation

RoboComp Component & Ros Node chatter